Prior to the manufacture and/or distribution of an electrical device (including a system or component such as a circuit board, integrated circuit, or system-on-a-chip (SOC)), the device is typically tested to determine whether it is built or functions as designed. Often, this testing is performed by an automated circuit test system (also known as automated test equipment (ATE)).
For the results of the test system to be meaningful, the system needs to be calibrated. That is, the intrinsic system errors that the test system may introduce during testing must be quantified.
To characterize the test system's intrinsic system errors, a calibrated driver may be sequentially coupled to each of the system's test signal comparators. A test signal initiated by the calibrated driver may then be read by each of the comparators; and the signals read by the comparators may be compared to an expected signal to determine their deviation therefrom. Likewise, a calibrated comparator may be sequentially coupled to each of the system's drivers. Test signals initiated by the drivers may then be read by the calibrated comparator; and the signals read by the calibrated comparator may be compared to an expected signal to determine their deviation therefrom.
In order to characterize a test system's intrinsic system errors using the above method, each of the system's drivers and comparators must be probed for the purpose of connecting it to the calibrated driver or comparator. One way to undertake such probing is via a robot that sequentially couples a calibrated testhead including a driver and a comparator to each of the test system's signal pins. However, such a robot is costly, and its mechanical tolerances are difficult to maintain.
Another way to undertake the probing of a test system's signal pins is via a relay signal selector. That is, a calibrated driver or comparator may be sequentially switched into contact with each of the system's drivers and comparators. However, relay signal selectors can cause signal degradation that makes system calibration difficult—especially during high-frequency AC timing calibration.